NEW YORK -- Playing for the first time in two months after spraining her left kneecap, seven-time Grand Slam champion Venus Williams beat Roberta Vinci of Italy 6-4, 6-1 Monday to reach the US Open's second round.

Williams landed awkwardly on her recently injured leg after hitting a swinging volley and grimaced. It was about the only glitch during her return to tennis.

"It was doing pretty good, till I landed on that leg on the swing volley. ... I was pretty happy to get through after not playing in forever," said Williams, whose younger sister Serena isn't playing in the U.S. Open after surgery for deep cuts on her right foot.

"It's not the same without two Williamses," the No. 3-seeded Venus added during an on-court interview. "I have big shoes to fill with just one Williams here."

Williams hit 10 aces, reaching 126 mph (203 kph), and became only the fifth woman with 200 career victories at major tournaments.

Vinci knew, of course, about Williams' recent time off, and said afterward with a sigh: "I hoped she would play worse."

Two of the American's Grand Slam titles came at Flushing Meadows, in 2000 and 2001, and other past US Open champions Roger Federer, Andy Roddick and Kim Clijsters also won on Day 1.

Federer hit a back-to-the-net, between-the-legs winner and fired 18 aces to eliminate Argentina's Brian Dabul 6-1, 6-4, 6-2 in a night match.

But 32nd-seeded Lleyton Hewitt, who won the tournament in 2001, hit 12 double-faults and was upset by 109th-ranked Paul-Henri Mathieu of France 6-3, 6-4, 5-7, 4-6, 6-1.

"I wasn't expecting a whole heap coming into this tournament, based on my preparation," said Hewitt, who had played only four matches, losing three, since Wimbledon.

Monday's loss is Hewitt's only first-round exit in 11 trips to the U.S. Open. Williams, meanwhile, improved to 12-0 in opening matches in New York, and 48-3 in openers at all major tournaments.

Williams hadn't competed since being upset in the Wimbledon quarterfinals June 29 by then-No. 82 Tsvetana Pironkova of Bulgaria. Pironkova won Monday, too, and Williams could face her in the third round.

That loss at the All England Club, shortly after Williams turned 30, led to talk about how much longer she can contend for major championships - and even how much longer she intends to play on tour. Yes, once you reach a certain age, birthdays tend to make you reflect on your own mortality. They also, in the case of professional athletes, tend to prompt questions about the state of your career.

Defending champion Clijsters briefly lost her footing on a windy day before recovering in time to win her 15th straight match at Flushing Meadows.

The second-seeded Belgian beat Hungary's Greta Arn 6-0, 7-5 after falling behind 4-0 in the second set. The 104th-ranked Arn had a chance to serve out the set at 5-4. But Clijsters got the break, then did it again to clinch the straight-set victory.

A year ago, Clijsters was a wild-card entry in only her third tournament back after 21/2 years away from the sport. Now she's one of the favorites to win the Open.

"Other players kind of didn't really know what to expect," Clijsters said.

The ninth-seeded Roddick celebrated his 28th birthday by beating Stephane Robert of France 6-3, 6-2, 6-2.

Roddick, who recently discovered he had a mild case of mononucleosis, was under doctor's orders to limit his physical activity, but he said he feels a lot better now than he did a month or so ago.

"It's going the right way," he said. "To be honest, once you decide to play, I think you throw all the excuses and everything else out the window. If I decide to play, then it's up to me to give 100 percent of what I have. So it's not something I really want to discuss too much from this point forward."

In an afternoon of mostly straightforward results, two-time French Open runner-up Robin Soderling of Sweden was stretched to five sets before edging 214th-ranked Austrian qualifier Andreas Haider-Maurer, who pounded 34 aces.

Other winners included No. 6 Nikolay Davydenko of Russia, No. 11 Marin Cilic of Croatia, No. 13 Jurgen Melzer of Austria, No. 17 Frenchman Gael Monfils and No. 22 Juan Carlos Ferrero of Spain, while No. 27 Fernando Gonzalez Chile quit in the third set of his match against Croatia's Ivan Dodig because of a knee injury.

Women moving into the second round included surprise 2009 U.S. Open quarterfinalist Melanie Oudin of the United States, French Open champion Francesca Schiavone of Italy, French Open runner-up Sam Stosur of Australia, two-time major finalist Elena Dementieva of Russia, Belarusian No. 10 Victoria Azarenka, No. 13 Marion Bartoli of France, No. 16 Shahar Peer of Israel, and No. 24 Daniela Hantuchova of Slovakia, who beat Russian former No. 1 Dinara Safina 6-3, 6-4.

Another past No. 1 now sitting way down in the rankings, No. 40 Ana Ivanovic of Serbia, reached the second round by eliminating Russia's Ekaterina Makarova 6-3, 6-2. (AP)